Torque control for rotary impact tool



Dec. 6, 1955 s. B. MAURER TORQUE CONTROL FOR ROTARY IMPACT TOOL Filed Dec. ll, 1951 INVENTOR. SPENCER B. MAURER BY RNEYv United States Patent TORQUE CONTROL FOR ROTARY IMPACT TOOL Spencer B. Maurer, Cleveland, Ohio Application December 11, 1951, Serial No. 261,063

16 Claims. (Cl. 192-.096)

This invention relates to portable, power-operated impact wrenches and similar tools for driving bolts, nuts, screws and the like, or for applying a rotational impact force to other objects, all such tools being hereinafter generically referred to as impact wrenches.

The usual tool of this character comprises three basic parts, namely: a prime mover, such as an air or electric motor; a rotatable hammer driven by the prime mover and having a high moment of inertia; and a rotatable output or work shaft, including an anvil member adapted to be struck by the hammer for imparting a high torque to the output shaft. The hammer member is disengageablev from the anvil member to permit the prime mover to rotate the hammer member freely for imparting a high angular momentum thereto, and a clutch mechanism is provided for repeatedly engaging the rotating hammer and the stationary anvil to apply the momentum of the hammer member to the anvil and to the output shaft. The clutch mechanism is also adapted to disengage the hammer from the anvil when the resistance to rotation of the output shaft has stalled the prime mover, thereby permit-ting free rotation of the hammer member for again building up its angular momentum. In the usual wrench this cycle of operation is repeated until the power to the prime mover is manually cut 0E. The tightness attained in the bolted assembly depends upon the length of time the tool is operated and the frictional condition of the threaded parts and other factors which are not easily: controlled by the operator. This means that the success of this type of assembly operation depends entirely on. the skill of the operator. In an attempt to solve this problem, two different rebound-typetorque control devices. have been built that regulate the maximum torque output of the wrench by means of a device operated by rebound energy.

One of these types is not reversible due tothe character of the rebound indicator. The accuracy of this type varies considerably due to internal motor friction and due to: variations in air pressure supplied to the motor. The other type requires the use of an energy accumulator between the motor and the hammer. This adds to the bulk and cost of the tool. One of these types shuts off the flow of power to the motor and the other interrupts the driving connection between the motor and the hammer as a means of stopping the tool when the predetermined. torque has been obtained. The first. of these requires an additional bulky air valve, and the second requires an extra set of clutch jaws in addition. to the normal impact jaws.

It is an object of the present invention to provide a rotary impact tool having an adjustable torque control mechanism which does not suffer from any of the previously mentioned disadvantages.

It isan object of the present invention to provide a rotary impact tool having an adjustable torque control mechanism which interrupts operation of the tool by preventing disengagement of'the impact jaws.

2,725,961 Patented Dec. 6, 1955 Another object of the invention is to provide an adjust able torque control mechanism which does not operate on rebound energy and which accordingly can be operated in either direction.

Another object of the invention is to provide an adjustable torque control mechanism which is independent in its operation of fluctuations in the power supply to the motor.

For a better understanding of the present'invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended. claims.

The device of this invention accomplishes this result by a torque sensitive mechanism which is driven by the hammer of the impact clutch and which, when the proper torque has been reached, interrupts the operation of the clutch or otherwise renders the tool inoperative until the tool is removed from the work.

One aspect of the present invention comprises a rotary impact tool having a rotary motor and a rotatable output shaft which includes. an impact-receiving surface. A rotatable hammer is provided including an impact delivering surface, and the hammer is driven by the motor. Clutch means move the impact delivering surface into engagement with the impact receiving surface to deliver a rotary impact blow to the impact receiving surface and move the impact delivering surface out of engagement with the impact receiving surface. Massive means are included in the rotary tool operable in. response to the decelerating forces exerted on the impact delivering surface during the impact blow to automatically render the tool inoperative when the decelerating forces on the impact delivering surface exceed a given value.

In another aspect of the invention, torque responsive means operate upon the attainment of a given amount of torque upon the output shaft. to render the tool inoperative by preventing theclutch means from moving the impact delivering surface out of engagement with the impact receiving surface.

In the drawings:

Fig. 1 is a cross-sectional view of a rotary impact tool embodying an adjustable torque control mechanism;

Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. l;

Fig. 3 is a cross-sectional view takenfalong line 33 of Fig. 2; and

Fig. 4 is an isometric view of a small portion of the impact tool.

With reference to. Fig. 1 of the drawing, the rotary impact tool comprises a housing lilwhich, for convenience in assembly, may be made in several sections and suitably connected together after assembly of the'tool within the housing.

An anvil i1 is rotatably mounted within the housing 16 and is journalled at 12 for rotarymotion with respect to the housing. An end of the anvil ii is square and protrudes outside of the housing and is provided with a locking pin 13 for connection to sockets which are well known in the art. The other end of the anvil 11 is provided with impact receiving surface 14, which is adapted to be engaged by impact delivering surface 15 comprising a portion of a massive hammer element 16. The hammer 16 is comprised of a cylindrical member 17 integrally connected to the impact delivering, surface 15 and adapted for rotation with a central spindle 13' and a cross valve member 19 which is carried by the spindle. Cross valve 19 is slidably mounted. in and is constrained to rotate in unison with the spindle 18 and has limited travel in a radial direction relative to the spindle. As shown in Fig. 3, the lug 23 onthe interior surface of cylinder 17 provides a driving connection with the spindle 1-8. The

spindle 18 has a hole 24 bored through it in a radial direction in which is slidably positioned the cross valve 19. The cross valve 19 is composed of a cylindrical valve portion and an eccentric weight 26 on one end. As is shown in Fig. 2, the cross valve member 19 has a clearance hole 20 extending through it, and through the hole 20 there extends a portion 21 of massive means 22. The massive means 22 is inserted in a central bore 29 at the rear end of spindle 18 and is mounted for rotation with, or relative to, the spindle 18 by means of the balls 27 and cooperating cam grooves 28 and 28 in opposed surfaces of the spindle 18 and the massive means 22.

The front end of spindle 18 is journaled in bore 30 of anvil 11 and is supported at its rear end by the cone driver 31 which in turn is supported on a protruding portion of the rotor shaft 32. The driving connection between the rotor shaft and the cone driver comprises interlocking spline teeth 33, and the driving connection between the cone driver 31 and the spindle 18 comprises a conical friction surface 34. Closure plate 35 is positioned within the rear end of the cylinder 17 and is held in place by retaining ring 36. A seal ring 37 effects a seal between the closure plate and the cone driver 31 prevents loss of com pressed air. The closure plate 35 rotates and moves axially with the cylinder 17. Rotor shaft 32 is journalled in ball bearings 40 and 41 mounted in the front end plate 42 and rear end plate 43 of the motor 44.

The motor is of the usual sliding vane and eccentric cylinder construction and is driven by compressed air supplied from the throttle through passageway 51 to a reversing cap 52 which supplies live air through annular passageway 53 to ports at the rear end plate 43 for either forward or reverse operation. Reversing cap 52 also contains a forward-facing internal bore 55 in which is mounted a portion of air tube 56. The air tube 56 extends from the bore 55 into one end of the hollow rotor shaft 32. An adjusting screw 57 is threaded into a central hole through air tube 56 and abuts on the forward end against spring button 58 which in turn is seated against spring 59. Spring 59 is mounted within the hollow rotor shaft and its fowrard end abuts against a rearwardly projecting portion of the massive means 22.

A portion of the live air which is supplied to the motor from the annular passageway 53 of the reversing cap 52 is conducted through passageways and 66 to chamber 67 at the rearward end of the air tube 56, thence down through a central hole 68 in the air tube 56 and through the hollow adjusting screw 57 radially outward through passageway 69 to the annular space 70 between the rotor shaft and the spring button 58 and again radially downward to a central hole 71 in the spring button and forward through and around the spring 59 to a central hole 72 in the massive means 22, then through a communicating hole 76 in piston into chamber 77 located in the forward portion of spindle 18.

As shown in Fig. 2, chamber 77 communicates through passageway 78 with an annular space 79 between hammer cylinder 17 and spindle 18. As long as the throttle 50 is open, live air is supplied to this chamber 79 and is confined within this chamber by seals 80 and 81. Fluid pressure within chamber 79 exerts a forwardly acting force on the hammer cylinder 17 and a rearwardly acting force on the spindle 18. The spindle 18, however, is not allowed to move in an axial direction while the hammer cylinder 17 is periodically moved forward and back in an axial direction to obtain the intermittent engagement and disengagement of the impact surfaces. Fluid pressure in chamber 79 also exerts a force on each end of cross valve 19. Since the diameter of the bore 24 at the head end of the cross valve is larger by several thousandths of an inch than the diameter at the opposite end of the cross valve, there is an inherent biasing force on the cross valve 19 tending to hold it in a retracted position so that the head 26 is radially inward toward the axis of the tool. Clearance hole 20 is vented to atmospheric pressure through axial holes 83 in massive means 22 and back through the grooves between the spline teeth 33 on rotor shaft 32 to annular chamber 84 in the front end plate 42, and from there radially outward through drilled passageway 85 to main exhaust passage 86. Groove 90, Fig. 3, on the small end of cross valve 19 forms a connecting passageway between the annular space 79 and drilled port 91 thus allowing live air to enter passageway 91 and to travel through angular hole 92 to a rear annular chamber 93 between the spindle 18 and the closure plate 35. Fluid pressure in this chamber, 93, exerts a rearwardly acting force on the hammer cylinder 17 and a forwardly acting force on the spindle 18. Since the spindle 18 is restrained from axial motion and also since the effective area of the closure plate 35 is greater than the effective area of the forward annular chamber 79, the rearwardly acting forces predominate and cause the hammer cylinder 17 to move in a rearward direction, thus causing disengagement of the impact delivering surface 15 from the impact receiving surface 14. This allows the motor 44 to accelerate, in a rotary direction, the massive hammer element 16. Eccentric head 26 of cross valve 19 soon attains sufiicient centrifugal force to overcome the air pressure bias which is acting on valve 19, causing the valve to move radially outward to the position shown in Figs. 2 and 3. In this position, the groove on the small end of the valve connects passageway 91 with the vented chamber 95 in the center part of the spindle 18. Thus the supply of live air to the rearwardly acting annular chamber 93 is cut off and this chamber is vented to the atmosphere through the angular hole 92 and the drilled port 91 thus dissipating any forces previously present on closure plate 35. This allows the engaging forces of the annular space 79 to again predominate and cause the hammer cylinder 17 to move forward so that the impact delivering surface 15 is again positioned to engage impact receiving surface 14 when the proper amount of rotation has occurred. When impact occurs between the hammer and the anvil, the hammer element 16 as a unit is decelerated by the resisting torque of the anvil as it tends to turn the nut or bolt that is being driven. The means for moving the impact delivering surface into engagement with-the impact receiving surface comprises the structure defining pressure chamber 79 and the crossvalve 19, and the means for moving the impact delivering surface out of engagement with the impact receiving surface comprises the structure defining pressure chamber 93 and the cross-valve 19.

Spring 59, acting through massive means 22 holds the piston 75 in engagement with valve seat 97 of the spindle. This confines the live air in chamber 77 and prevents this air from entering the annular chamber 98 between the piston 75 and the spindle 18. There is sufficient clearance 99 between the O. D. of piston 75 and the I. D. bore of spindle 18 to allow a small rate of leakage from chamber 98.

While the tool is operating on a nut or bolt which turns readily, the massive means 22 is coupled to the hammer 16 by means of the force of the spring 59 acting through balls 27 and inclined grooves 28, 28. When the nut or bolt does not turn readily, causing the tool to tend to exceed a set maximum torque output, the massive means becomes uncoupled from the hammer as the inertia of the massive means overcomes the torsional force of the spring exerted on the massive means through the balls 27 and cam grooves 28, 28. When the massive means overrides the hammer the balls 27 roll between the opposing cam grooves 28, 28' causing the massive means to. move axially in a rearward direction along a helical path parallel to the path of the cam grooves. The movement of the massive means 22 in the. rearward direction causes the seating force to be removed from the valve seat 97 and allows air from chamber 77 to enter into chamber 98 at a rate great enough to exceed the leakage from this chamber through clearance 99 f -K n answer thus applying an overbalancing fluid pressure force against the forward end of piston 75 which forces the massive means 22 to move rearwardly' against spring 59 until the rear portion of piston 75 contacts the side of sliding cross valve 19; Thisprevents any further compression of spring 59- and sets up a high frictional or binding force on the cross valve 19, thus preventing the normal air biasing force from retracting said valve. This prevents disengagement ofthe impact surfaces and maintains the unit in a stalled condition until throttle valve 50 is manually closed.

When throttle valve 50 is manually closed, all air beyond the throttle valve is dissipated through previously mentioned exhaust channels and clearances, thus allowing the spring 59 to return the massive means 22 and the piston 75 to their original position so that a seal is again established in the valve surface 97. When the throttle is again opened, the tool will again operate in a normal fashion producing repeated impact blows until the force of said blow and, consequently, the rate of deceleration of the hammer again becomes sufiicient to cause the massive means 22 to rotate forwardly ahead of the spindle, again causing the control mechanism to operate.

The torque at which the control mechanism operates can be varied by varying the initial force of spring 59. A slot 100 in the rear end of adjusting screw 57 can be reached from the rear of the tool by removing plug 101, and a screwdriverinsertedl in said slot is used to turn the screw either forwardly in to increase the spring pressure or in the opposite direction to reduce the spring pressure.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those sldlled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. In a rotary impact tool; a rotary motor; a rotatable output shaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; means for moving said impact delivering surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; and massive means operable in response to the decelerating forces exerted on the impact delivering surface during said impact blow for automatically rendering the tool inoperative when the decelerating force on said impact delivering surface exceeds a given value.

2. A rotary impact tool as set forth in claim 1, further characterized by means mounting said massive means for rotation under driving forces from said hammer and for overriding the motion of said hammer, resilient means biasing said massive means and said hammer together to cause said massive means to rotate in unison with said hammer until the said decelerating force exceeds said given value.

3. A rotary impact tool as set forth in claim 1, further characterized by said hammer and said massive means being axially mounted with respect to each other; said hammer having a helical groove with a closed end and said massive means having a helical groove facing the groove in said hammer and having a closed end 0pposite the closed end of said hammer groove establishing a helical ball race, ball means retained in said helical race, said resilient means biasing said massive means and said hammer together to confine said ball means between the two closed ends of said grooves to establish said driving connection, and upon said overriding action to cause said closed ends of said grooves to separate and to cause said ball means to roll between the opposed surfaces of said two grooves to cause said hammer and said 6 massive means tomoveax-iaily with respect to each other to overpower the bias of'said' resilient means.

4. A rotary impact-tool set forth in claim 2, further characterized by means for adjusting the biasing force of said resilient means. to change the decelerating force at which said massive means overrides the motion of said hammer.

5. A rotary impact tool as set forth in claim 4, further characterized by said resilient means comprising a spring;

6. A rotary impact tool as set forth in claim 5, further characterizedby said resilient means comprising a spring and air pressure means.-

7. Ina rotary impact tool; a rotary motor; a rotatable output shaft including -an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; actuating means for moving said impact delivering surface into engagement with said pact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; and torque responsive means operable upon the attainment of a given amount of torque upon said output shaft for rendering said tool inoperative by preventing said actuating means from moving said impact delivering surface out of engagement with said impact receiving" surface.

8. In a rotary impact tool; a fluid driven rotary motor; a rotatable outputshaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said' motor; means for moving said impact delivering. surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; valve means; massive means associated with said valve means andoperable in response to the decelerating forces exerted on the impact delivering surface" during said impact blow for opening said valve means; piston means connected to said valve means and actuated by fluid when said valve is opened for maintaining said valve open; means for rendering said tool inoperative upon said valve opening; and resilient bias means exerting a force against said massive means for maintaining said valve means closed until opened by said massive means when the decelerating force on said impact delivering surface exceeds a given value.

9. A rotary impact tool as set forth in claim 8, further characterized by means for adjusting the said resilient bias means to change the given value of the decelerating force at which said valve is opened by said massive means.

10. A rotary impact tool as set forth in claim 9, further characterized by said resilient bias means comprising a spring.

11. A rotary impact tool as set forth in claim 10, further characterized by said resilient bias means comprising a spring and air pressure means.

12. In a rotary impact tool, a fluid driven rotary motor; a rotatable output shaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; means for moving said impact delivering surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; massive means mounted for rotation around the axis of said hammer and for overriding the motion of said hammer; resilient bias means biasing said massive means and said hammer together to cause the massive means to rotate in unison with said hammer until decelerating force on said hammer during impact exceeds a given value; cam means located between said hammer and said massive means for moving said massive means axially with respect to said hammer against said bias during said overriding motion; and

means responsive to said axial motion of said massive means to prevent further operation of said means for moving said impact delivering surface.

I 13. In a rotary impact tool, a fluid driven rotary motor; a rotatable output shaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; means for moving said impact delivering surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; massive means mounted for rotation around the axis of said hammer and for overriding the motion of said hammer; resilient bias means biasing said massive means and said hammer together to cause the massive means to rotate in unison with said ha mer until decelerating force on said hammer during impact exceeds a given value; cam means located between said hammer and said massive means for moving said massive means axially with respect to said hammer against said bias during said overriding motion; and means responsive to said axial motion of said massive means to prevent disengagement of the impact surfaces.

14. In a rotary impact tool; a fluid driven rotary motor; a rotatable output shaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; means for moving said impact delivering surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; massive means mounted for rotation around the axis of said hammer and for overriding the motion of said hammer; resilient bias means biasing said massive means and said hammer together to cause the massive means to rotate in unison with said hammer until decelerating force on said hammer during impact exceeds a given value; cam means located between said hammer and said massive means for moving said massive means axially with respect to said hammer against said bias during said overriding motion; and means responsive to said axial motion of said massive means to prevent disengagement of the impact surfaces until the fluid supply to said motor is cut off.

15. In a rotary impact tool; a rotary motor; a rotatable output shaft including an impact receiving surface; a rotatable hammer including an impact delivering surface driven by said motor; means for moving said impact delivering surface into engagement with said impact receiving surface for delivering a rotary impact blow to said impact receiving surface and for moving said impact delivering surface out of engagement with said impact receiving surface; and rotatable massive means driven with said rotatable hammer and operable in response to the decelerating forces exerted on the impact delivering surface during said impact blow for overriding said hammer and rendering the tool inoperative when the decelerating force on said impact delivering surface exceeds a given value.

16. A rotary impact tool as set forth in claim 15, further characterized by said massive means rendering said tool inoperative by maintaining said rotatable hammer in engagement with said impact receiving surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,128,761 Thomas Aug. 30, 1938 2,143,173 Shaff Ian. 10, 1939 2,160,150 Jimerson et al. May 30, 1939 2,261,204 Amtsberg Nov. 4, 1941 2,293,787 Worden Aug. 25, 1942 2,326,347 Forss Aug. 4, 1943 2,476,632 Shaff July 19, 1949 2,484,364 Whitledge Oct. 11, 1949 2,580,607 Schmid Jan. 1, 1952 

